Oak Tree Help

To Keep Your Mature Oaks Healthy and Happy

or Help a Stressed, Unhealthy Oak Back to Health:

Check for these:

Summer water

Assess the area; find out if the oak is receiving summer
water. If a mature oak is, receiving summer irrigation,
gradually
decrease the summer water until there is no summer water.
Lawns and drip irrigation are a
big NO NO!

Weeds

Find out what is growing under the oak; there may be a
mixture
of native and non-native, or alien, plants. You want to
remove the
alien plants and keep the native plants. See weeds.

Some of the oaks in California can be hundreds of years old, then we put a lawn under them. Oaks will commonly do fine with a conventional lawn or garden under them for about 10 years, then they get buggy and start to die. Their immune system and root structure is compromised. Sometimes you can get them back to degree of health, sometimes not. After a lawn or English garden, they are like an aids patient.

Plant community

Plant associated shrubs that usually live alongside or
under
oaks. Check individual listings under specific oaks. To
learn more see
the Plant
community pages.

Mulch

Let the natural oak mulch
build up
under the tree, by removing the weeds.

34 years later. We took the driveway out that used to be under the trees, mulched the trees and planted under story. Trees doubled in size.

DO NOT FERTILIZE oak trees (under any circumstances)!

Fungicides and insecticides

Do not spray
fungicides
or insecticides on oak trees. There are a lot of
good fungi on the
oak that the Oak requires to survives. Many insects play
an important
role in the ecology of the oak tree. 'Bad insect”
population
explosions are usually a sign of bad ecology. In most
cases you are
only removing the symptom by spraying the insects!

Pruning

Do not prune mature
oak trees. (light pruning is OK so that you can walk under
the oak or
so the limb is in not in danger of falling on your house,
car or
person.) Remember, many birds nest in cavities in the dead
branches.

You can help the
birds after your yard or hillside planting
establishes itself by
wandering the streets gathering acorns to throw under your
bushes. This
achieves several objectives: you get baby oaks under your
bushes, you
can talk to every cop in town, (nobody knows what to do
with hikers in
towns anymore), your neighbors will start referring to you
as the
weirdo that's hanging around under the trees, you'll learn
where all
the oaks and dogs on the street are, and if you gather on
your day off
everyone will know you're unemployed, life will not be
boring! AND
you'll get your exercise running from the dogs!

Fog drip and weeds

On Vandenberg Air Force Base it has been documented in
one
stand of Tanbark
Oaks,
Lithocarpus densiflorus, that the rainfall is
14
inches; but the fog drip is 38 inches, and total
precipitation is 52
inches. If weeds get under the oaks the fog drip is almost
entirely
lost (the weeds capture it for themselves), and most of
the trees
immune system (the roots are protected by a group of fungi
called
mycorrhiza) collapses and pathogens start replacing the
mycorrhizal
links on the roots. We used to think the trees could
tolerate some
weeds; we now think they can tolerate hardly any. It
appears that the
slower-growing oaks like Blue
oaks Quercus
douglasii, Quercus
parvula, most of the other Scrub
oaks and Quercus
X alvordiana may
only be able to tolerate 10% or less weed coverage under
the oak from
the trunk out to double the drip line in distance. At 10%
weed coverage
oaks slow their growth and acorn production. At about 30%
weed coverage
most oaks start declining. As little as 5% weed coverage
may allow them
to be increasingly susceptible to Sudden Oak Death.

Here is fog drip on an apple tree. On an oak tree the leaf absorbs much of the moisture and the drip is less.

Fire Note: Oaks by themselves are relatively fire safe; add weeds
under them and they become a 100 foot fireball.

Weeds kill Oaks

Usually, in the central coast ranges, there are massive
amounts of alien annual grasses growing under oaks. These
alien plants
choke the life out of the oaks. Remove alien annual
grasses from under
oaks at the same time trying not to disturb the soil.
Pretty hard, huh?

Herbicides

Specific herbicides
that target grass work well (Don't spray the native
grass.) Other
sprays can be used to kill star thistle and other nasties.

Weedeating

Weedeating is like scraping the pus off of a wound, it
really
is not healing the wound, the weeds are still there! (It
does reduce
weed numbers though, if you weedeat before the weeds set
seed)
weedeaters aren't exactly selective either. You will have
trouble
weedeating the weeds and not the natives.

Healthy leaf litter under a Blue oak. Blue oaks, like a different set of plants under them than coast live oaks.

Pulling the weeds by hand?

This causes soil disturbance, and at the same time,
encourages
gophers to move into the area, eating everything that
takes their fancy
(this means almost any living plant!) and provides a
perfect seed bed
for the alien annual grasses. If you pull the weeds
by hand,
afterwards, place tree chippings from the local arborist
or utility
company, preferably mostly oak, on the soil, if there is
no mulch
layer. This will work as a good mulch until the tree
produces enough of
its own mulch, to make a nice thick, at least 2 inch
layer. Or just
keep pulling the weeds, trying to disturb the soil as
little as
possible every year until the mulch layer naturally builds
up. Good
luck!

How do you deal with so many weeds? Think small. Weed or spray a small area, then mulch and plant that area before you do the next.

Healthy Oak Leaf Litter-why is healthy oak leaf litter
important to the
health of the oaks?

Because the group of microorganisms that live in this
area,
where the oak leaves meet the soil, are responsible for,
among other
things, protecting oaks from diseases, (the microorganisms
produce
specific antibiotic and antifungal agents, produce food
for the
free-living microorganisms that attack disease organisms)
and providing
oaks with nutrition and moisture. These microorganisms
extract
nutrients and water from the oak leaves as they slowly
break down some
of the leaves, at the same time preventing the breakdown
of most of the
leaves, and holding them in so-called 'storage', to be
broken down as
needed. When the oak leaf litter layer is replaced by
alien plants and
their litter (dead alien plant parts on the ground) the
oak tree loses
a large portion of its disease protection, nutrients and
water. The
weeds take the water and nutrients that would otherwise be
used by the
oak and its associated microorganisms. There! So the tree
has lost a
good portion of its disease protection, food and water.
Also, now that
the group of microorganisms that lived in the oak
leaf-bare soil
interface, is weakened because their tiny habitat has
turned into a
mass of weeds, and they cant access the nutrients and
water as before,
it is not functioning well and cannot provide protection
to the oak
tree from disease.

The oak tree is obligately mycorrhizal. That means if the
fungi ( the dominant group of microorganisms that are part
of the
specific group of microorganisms that live in this
mini-habitat, in
cooperation with the oak, are unhealthy, and they start
dying, then the
oak tree dies. The oak tree can not live without the
fungi. That is why
oak leaf litter is crucial to the health of the oak tree.
There are
many species of microorganisms that live just on and with
one oak tree,
and different species live with trees at different points
in the oaks'
development. To put it simply, remove the weeds, let the
oak leaves
fall and form a thick, soft, moist mulch and voila, the
microorganisms
and, in turn, the oak tree, will be healthier. Mulch
cannot work alone,
though. Oh, did I mention associated plants? There are
many species of
native plants that live under the canopy of the oak. If
the plants are
present, that is great. If they are not present, then that
area will be
very difficult to maintain free of weeds. Replace the
weeds with the
oak leaf litter AND the oak's associated plants.

As an analogy, weeds are like a staph infection in a
human
body. Your body can tolerate a small quantity of this
infection and
your immune system will suppress the bacteria. If the
bacteria pulses
your body you probably will die if not treated immediately
with
antibiotics. Scraping the bacteria off of your arm or leg
doesn't
remove it, it just makes more entry points. Weeds in a
native system
behave the same way. Kill the suckers with herbicides
(analogously,
antibiotics) if possible. Hand pulling the weeds usually
makes more
infection points; that is, it disturbs the soil, which
makes a perfect
seed bed for more weeds (remember, they thrive on
disturbance) and gets
the gophers all excited, and making new burrows, and
eating lots of
plants that you wanted to save, but it does remove the
weeds. Again,
try to hand pull the weeds with the least soil disturbance
possible.
The native oak mulch layer is VERY,VERY important. It is
like the
body's skin. It is very important that it remain native
and
undisturbed. If you're planting plants under oaks, make
sure the plants
are native under oaks. Non-native plants under an oak are
weeds to the
oak, and rob the life out of the oak and allow pathogens
and herbivores
to target the oak in many pathways that seem completely
inconsistent,
such as deer eating your oak tree, but not the oaks nearby
with no
weeds under them. The weeds are considered an alternate,
competitive,
non-cooperative ecosystem with a completely different set
of pathogens,
energy collection, and life strategies. Much of the native
wildlife
that depends upon the live oak trees usually leave before
the oaks die.
So, if you want healthy oaks and wildlife, kill the weeds!

A poor Valley oak in the Riverdale area. No understory, no mulch, a tree that's barely alive.

We get at least one city person a year that asking why all of our oaks are dead. The blue oaks and valley oaks are deciduous here in winter.